This invention relates to apparatus that uses ultrasound to produce images of a section of an object such as the human anatomy.
B-scans and real-time scans are among the ultrasound apparatus operational modes for obtaining images. In the B-scan mode, a transducer, usually a single piezoelectric crystal, is moved along the body surface in a single plane while the transducer emits a pulsed beam of ultrasound and receives echos from wherever there are density discontinuities or impedance changes in the body as is well known. The echo energy is converted by the transducer to electric signals which can be organized in a manner that enables an image of the plane that is traversed by the beam to be reconstructed or displayed. B-scanners support the transducer on an arm assembly of two or three pivotally connected segments which constrain the transducer to move in a single plane, so the reconstructed image is a view of a slice through the anatomy.
The arm segments are provided with position-sensing elements for providing data indicative of the origin and the direction of any beam originating from the transducer. If the transducer is periodically excited and the reflected data is stored in a memory array at locations corresponding to the position of the transducer at the time of the pulse, then, as the transducer is moved along the body, the echo data will fill the array to provide a final composite picture.
In systems to which the present invention is pertinent, the echo signals representative of picture elements (pixels) for a single ultrasound scan, after suitable processing and digitization, are stored in a memory array. The memory array and its affiliated controls provides for converting the digital pixel signals to analog video waveforms on a line-by-line basis to enable displaying the image on a cathode ray tube screen. B-scanning is not, however, suitable itself for picturing moving parts of the anatomy, such as the heart, which is in motion due to beating or the thorax which is in motion due to breathing.
Real-time imaging is now accomplished by using a linear array to form a rectilinear image, or using a mechanically oscillated or rotated transducer(s) to form a sector image or using a phased array transducer to electronically steer the ultrasound beam to form a sector image. In all of these methods ultrasound beams are directed through a region of the anatomy at a rate sufficiently fast to make the continually updated echo data appear live in the display. As is well known, linear array transducers are composed of a series of juxtaposed similar piezoelectric elements on the order of about 64 elements, for example. The elements are pulsed with high voltage in some orderly and repeatable sequence to cause them to emit ultrasound pulses that result in corresponding echo signals which are addressed to the scan converter memory array and are continuously updated or refreshed at a high rate so a real-time or motion-indicating image can be displayed.
A significant deficiency in prior art real-time scanning systems is that only an image of a slice of anatomy which is under the transducer is displayed. When the transducer is moved along the body surface to obtain an image of an adjacent region in the anatomy, the previous image disappears from the display. Thus, the viewer must exercise judgment, based on general knowledge of anatomy, as to where any image is located in the anatomy. In other words, there is nothing to which the real-time image on the display can be referenced to determine its location more exactly relative to surrounding anatomy. For instance, a sector scan transducer might be rocked or a linear array transducer might be scanned along a body in search of a tumor which, when located, the physician might want to palpate and observe in real-time on the display screen. In such case it would be desirable if the physician were able to observe where the tumor is located relative to other parts of the anatomy. Heretofore, it has not been possible to do this on a single display screen. The difficulty is accentuated where, as on many occasions, the person who made the scan and recorded it is not the same as the person who must display it and interpret it at a later time. Having a real-time or active region embraced by static views of surrounding anatomical regions would be particularly valuable under these circumstances. Moreover, real-time images are more likely to be misinterpreted at any time that the interpreter is not positive about where the image has been taken.